Selectively positioned interposed vertical transfer gap



June 24, 1969 w A, CARTER 3,452,173 I SELECTIVELY POSITIONED INTERPOSED VERTICAL TRANSFER GAP FiQled March 25. 1966 v I Sheet 1 of 2 I I I O :1

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June 24, 1969 w. A. CAR ER I 3,452,173

SELECTIVELY POSITIONED INTERPOSBD VERTICAL TRANSFER GAP Filed March 25. 1966 Sheet 2 or? INVENTO R. W/L/4/W 6 5%[755 United States Patent U.S. Cl. 200-147 2 Claims ABSTRACT OF THE DISCLOSURE A circuit breaker is disclosed including a pair of cooperating contacts above which is positioned an arc chute to extinguish an are drawn between the contacts upon separation thereof. Front and rear arc runners are positioned at opposite interior ends of the arc chute and a face-wound blowout coil is diposed on at least one surface of the arc chute in a configuration which defines an area which encompasses the front and rear arc runners. A vertically interposed transfer gap assembly is selectively positioned vertically above the separating contacts and at a predetermined location with respect to the front and rear arc runners such that the transfer time between the separating contacts and the vertical transfer gap is minimized while at the same time the potential difference existing between the rear arc runner and the transfer gap will be minimized.

This invention relates to air magnetic circuit breakers, and more particularly relates to such circuit breakers which include an interposed vertical transfer gap selectively positioned within the arc chute of such circuit breaker.

The type of circuit breaker to which the instant invention is applicable generally includes a pair of separating contacts, usually designated as stationary and movable, above which is positioned an arc chute into which the are drawn between the separating contacts may be urged for the elongation and ultimate extinguishment thereof. The are chute has a front and rear arc runner positioned at the opposite ends thereof with the front are runner being electrically connected to the lower main terminal of the circuit breaker while the rear arc runner is normally electrically isolated from the upper main terminal and stationary main contact of the breaker by a jump gap assembly which normally includes a plurality of spaced apart metallic plates. Included within the arc chute is a magnetic blow out coil electrically connected between the upper main terminal of the breaker and the rear arc runner such that upon separation of the cooperating contacts initial detonation of an arc drawn between will cause one end of the arc to be transferred from the stationary contact to the rear arc runner whereby the blow out coil will be energized to generate magnetic flux which cooperates with the drawn are to urge such are up into the arc chute for extinguishment. Further movement of the movable contact causes the other end of the arc to be transferred to the front are runner whereby the interaction of the magnetic flux from the blow out coil and the arc itself causes the ends of the arc to be propelled up the arc runners while the central portion of the arc is elongated through a tortuous path established by a plurality of the arc plates within the arc chute assembly.

More recent circuit breakers have proposed that the transfer gap between the stationary contact and the rear arc runner be eliminated that such a transfer gap be vertically interposed within the arc chute assembly itself. Such vertically interposed transfer gaps have generally been of two configurations. The first configuration may be represented by the circuit interrupter shown in US. Patent 2,590,602 issued to R. E. Frink on Mar. 25, 1952, and the second configuration may be illustrated by US. Patent 2,616,007 issued to R. C. Dickinson et al. on Oct. 28, 1952.

In the circuit breakers illustrated by the Frink patent, the vertically interposed arc runner and a conducting probe which is spaced between two adjacent arc plates of the arc plate assembly at a predetermined distance from the rear arc runner. The Frink interrupter includes magnetic blow out coils, the terminals of which are electrically connected to the rear arc runner and conducting probe, respectively, such that upon transfer of the drawn arc to the front and rear arc runner, the portion of the are extending between the rear arc runner and the conducting probe inserts the magnetic blow out coil in the circuit of the arc. At an initial period, the coil is in electrical parallel with the arc existing between the rear arc runner and the conducting probe. Upon extinguishment of that portion of the are extending between the rear arc runner and the conducting probe, the magnetic blow out coil remains in series with the portion of the are extending between the conducting probe and the front are runner whereby the flux generated by such coil urges the remaining are into the arc chute assembly for extinguishment thereof.

In the circuit breaker illustrated by the Dickinson et al. patent, the vertically interposed transfer gap assembly comprises a pair of transfer gap runners spaced midway between the ends of the arc chute assembly in which the vertically interposed transfer gap is located. Residing between such transfer gap arc runners is the central portion of a magnetic member about which is located a coil, the ends of which are electrically connected to the transfer gap arc runners. Also located between the transfer gap arc runners, but below the magnetic member and coil, are a plurality of metallic plates which, together with depending portions of the transfer gap arc runners, extend below the arc plates which define the main arc chute assembly. Upon separation of the cooperating contacts, the initial detonation of the are drawn therebetween causes a central portion of such arc to extend between the transfer gap arc runners whereby the magnetic blow out coil is then inserted, initially in parallel, with that portion of the arc extending between the transfer gap arc runners. Upon extinguishment of the central portion of the are extending between the arc runners, the blow out coil is in series with the remaining end portions of the arc which extend between the rear arc runner and one of the transfer gap arc runners, and the front are runner and the other of the transfer gap arc runners whereby the flux generated by the blow out coil urges such arc end portions into the arc plates disposed on both sides of the transfer gap assembly for ultimate extinguishment thereof.

Both the breakers illustrated by the Frink and Dickinson et al. patents suffer from serious disadvantages which the instant invention effectively eliminates. Specifically, with respect to the interrupter illustrated by the Frink patent whereby the vertically interposed transfer gap assembly comprises the rear arc runner and a spaced apart conducting probe; the location of such vertical transfer gap assembly at the rearmost portion of the arc chute assembly materially lengthens the space between the separating contacts and such transfer gap assembly such that the time necessary for the transfer of the are drawn between such contacts to the vertically interposed transfer gap assembly is materially increased, with the total time of ultimate circuit interruption being correspondingly increased. Obviously, the time lag of arc transfer and circuit interruption caused by the hidden location of such far removed transfer gap assembly increases the transfer gap comprises the rear length of time during which the drawn arc exists and thereby undesirably hastens contact erosion while at the same time facilitating excessive build up of ionized gas contamination which increases the chance of restrike, and as an ultimate consequence, builds up the pressure of such gases to dangerous explosion levels.

Furthermore, when the teachings of a1 breaker such as that shown in Frink are extended to a circuit breaker which might include a face wound blow out coil, that is, a coil which encompasses an area including both the front and rear arc runners, the fact that one end of the coil in the Frink patent would be electrically connected to the upper or high potential terminal of the circuit breaker would cause the entire face wound blow out coil to float to a potential appearing on such high potential terminal. Since a portion of the face wound blow out coil passes extremely near the front are runner which is electrically connected to the low potential terminal of the breaker, it becomes apparent that with the cooperating contacts separated, the full system potential existing between the upper and lower main terminals of the breaker will exist across the space which exists between the front are runner and the portion of the face wound blow out coil which passes closely thereto. In such an embodiment the potential gradient across such air space would cause corona about the front are runner and in the ultimate situation could cause an arc to be stricken between the coil and the front are runner. As a necessary consequence of a design which incorporates a face wound blow out coil in the Frink circuit breaker, it follows that the maximum impulse level for such a breaker cannot be increased beyond a predetermined level dependent upon the distance of the front are runner from the face wound blow out coil.

With respect to the disadvantages inherent in a breaker constructed in accordance with the Dickinson et al. patent, that is, where the vertically interposed transfer gaip assembly is spaced midway in the arc chute assembly, it is noted that although the transfer gap assembly is selectively located so as to minimize the distance between the stationary contact and the transfer gap arc runners, and thereby hasten transfer of the arc to the transfer gap assembly; the location of such transfer gap assembly in the center of the arc chute assembly still results in a disadvantage which is both highly dangerous and contrary to efficient arc interruption. Specifically, since the rear arc runner is electrically connected to the high potential main terminal of the breaker, and since the front arc runner is electrically connected to the low potential main terminal of the breaker, it may be approximated that the entire system voltage between the high and low potential main terminals of the breaker appears across the arc chute assembly spaced between the front and rear arc runners. Thus when the vertically interposed transfer gap assembly is located in the center of the arc chute assembly it may be approximated that half the total system potential exists between the rear arc runner and the rearwardly located transfer gap arc runner and half the total system potential exists between the front are runner and the forwardly disposed transfer gap arc runner.

As noted previously, the transfer gap arc runners of the Dickinson et al. patent extend partially below the arc plates which comprise the main arc chute assembly, and hence the rearwardly disposed transfer gap arc runner is dangerously close and exposed to the rear are runner of the breaker. With half the total system potential appearing across these two members it is extremely possible that after circuit interruption a restrike is possible therebetween. Assuming the existence of such a restricken are, it becomes apparent that the total system potential will now exist on the space between the front are runner and the forwardly disposed transfer gap arc runner, whereby an are between these two members would be almost certain to occur. Thus a process which initially began as .an are between the rear arc runner and the rearwardly disposed transfer gap arc runner, followed by the striking of an are between the front arc runner and the forwardly disposed transfer gap arc runner, would result in the complete reignition of the are which was to be interrupted by the arc chute assembly.

Furthermore, it should be noted that the transfer gap assemblies constructed in accordance with the teaching of Dickinson et al. comprise metallic plates interposed between the transfer gap arc runners to aid in extinguishment of that portion of the arc which exists therebetween. Such metallic plates contribute to gas contamination which suffer from the disadvantages noted above, and, furthermore, reduce the quantity of arc voltage available during interruption for transfer of the arc current into the blow out coil.

In contrast to the circuit breakers illustrated by the Frink and Dickinson et al. patents, the instant invention comprises a circuit breaker including a pair of cooperating contacts; an arc chute positioned above such contacts to extinguish an arc which is drawn between the contacts upon separation thereof; front and rear arc runners positioned at opposite interior ends of such arc chute; a face wound blow out coil which is disposed on at least one surface of the arc chute in a configuration which defines an area which encompasses the front and rear arc runners; and a vertically interposed trans-fer gap assembly which is selectively positioned between two adjacent arc plates of the main arc chute assembly at a predetermined location within the arc chute assembly to minimize the time required for the drawn arc to transfer to the arc runners of such vertically interposed transfer gap assembly, while at the same time minimizing the potential difference which exists between the rear arc runner and the rearwardly disposed transfer gap are runner so as to minimize the possibility of a restrike therebetween.

Specifically, the transfer gap assembly is positioned immediately above the separating contacts so as to establish the minimum possible distance between the separating contacts and the arc runners of the transfer gap assembly to thereby avoid the time lag which is inherent in the transfer of an are from the separating contacts to the transfer gap assembly such as that shown in the Frink patent. Simultaneously, the transfer gap assembly is located at a predetermined position within the main arc chute assembly, in the preferred embodiment approximately one-quarter of the distance between the front and rear arc runners of the circuit breaker, so that ap proximately only one-quarter of the total system voltage appears between the rear arc runner of the circuit breaker and the rearwardly disposed transfer gap arc runner, thereby reducing by 25% the potential which appears between such members in a circuit breaker constructed in accordance with the Dickinson et a1, patent. Such reduced potential impressed between these two members reduces the possibility of restrike therebetween.

As a further feature of the instant invention the ends of the face wound magnetic blow out coil are electrically connected to the front and rear transfer gap arc runners, respectively (one end thereof not being connected to the rear arc runner as in the Frink patent), so that after circuit interruption the blow out coil is free to float to some independent potential determined by the capacitive coupling of the blow out coil to either the front or rear arc runners and ground, also taking into account the leakage resistance to such points. The fact that the blow out coil is free to float to a potential, not necessarily the same potential appearing on the rear arc runner, results in a reduced potential gradient appearing between the front are runner and the portion of the blow out coil which passes nearby. As a result of the reduced potential gradient between these members, corona formation on the front arc runner is reduced and the ultimate possibility of restrike therebetween is virtually eliminated. Finally, with respect to the electrical coordination of the transfer gap arc runners and the ends of the blow out coil, it is noted that the connections between the coil ends and the transfer gap arc runners are located outside and above the area encompassed by the face wound blow out coil so as to improve the dielectric integrity of the final assembly.

As another feature of the instant invention, the cooperation of a face wound blow out coil and a vertically disposed transfer gap assembly results in the transfer gap assembly being intercepted by the flux generated by" the face wound blow out coil. Thus that portion of the drawn are which at an initial period exists between the front and rear transfer gap arc runners will be urged b the magnetic flux up into the space between such transfer gap arc runners to hasten extinguishment of such are portion and thereby quickly establish the introduction in series of the blow out coil.

With respect to the space between the transfer gap arc runners, it is contemplated by the instant invention that such transfer gap arc runners be spaced apart by ceramic plates which are of identical construction as the arc plates which form the remainder of the main arc chute assembly, thus materially reducing cost, simplifying assembly, while at the same time hastening the extinguishment of the are which initially exists between the transfer gap arc runners. Furthermore, the ceramic plates spaced between the transfer gap arc runners (as opposed to metallic plates as taught in the Dickinson et al. patent) virtually eliminate gas contamination and at the same time permit a larger quantity of the arc voltage available during interruption to be used for the transfer of the fault current into the blow out coil.

The resultant circuit breaker permits short arcing time, thereby reducing contact corrosion and consequential gas contamination; reduces the possibility of a restrike between the transfer gap arc runners and the front and rear arc runners of the circuit breaker; reduces the potential gradient of the space between the front arc runner and the face wound blow out coil; decreases manufacturing costs; and allows an increase in the critical im pulse level for the entire circuit breaker.

Accordingly, it is an object of the instant invention to provide a circuit breaker having an arc chute assembly positioned above a pair of separating contacts wherein such arc chute assembly includes a vertically interposed transfer gap positioned between the adjacent are plates of the arc chute assembly at a predetermined position Which minimizes the time required for an arc to reach such transfer gap assembly while at the same time minimizes the potential difference existing between the rear arc runner of the circuit breaker and the transfer gap assembly.

It is a further object of the instant invention to provide such a circuit breaker wherein the predetermined position for the transfer gap assembly is closer to the rear arc runner than the front are runner, preferably at a distance of one-quarter the space existing therebetween.

It is a further object of the instant invention to provide such a circuit breaker in combination with a face wound blow out coil wherein the ends of such blow out coil are electrically connected to the transfer gap arc runners rather than the rear arc runner of the circuit breaker, thereby permitting the blow out coil to float after interruption to a potential which is substantially less than the system voltage appearing across the main terminals of the circuit breaker.

It is a further object of the instant invention to provide such a circuit breaker wherein the transfer gap assembly is positioned to intercept the flux generated by the face wound blow out coil and wherein the transfer gap arc runners of such transfer gap assembly are spaced apart by at least one arc plate which is of identical construction to the ceramic arc plates of the main arc chute assembly, thereby facilitating extinguishment of a portion of the arc initially existing between such transfer gap arc runners, reducing gas contamination, and increasing the quantity of arc voltage available during interruption for transfer of the fault current into the blow out coil.

Other objects and a fuller understanding of the invention may be had by referring to the following description and drawings, in which:

FIGURE 1 is a side view of a single phase of a circuit breaker embodying the vertical transfer gap of the instant invention; and

FIGURE 2 is an exploded perspective view of a preferred construction of the vertical transfer gap of the instant invention.

Referring to FIGURE 1, there is shown a side view of a single phase of a circuit breaker 10 which embodies the instant invention. Although the instant invention will be described with respect to a single phase, it is to be understood that the instant invention is equally applicable to circuit breakers having any number of phases, recognizing that if more than one phase is present the structure to be presently described would be present in each of such plurality of phases. Circuit breaker 10 includes upper and lower main terminals 12 and 14, respectively, to which the line being protected is connected. Secured to one end of upper terminal 12 is stationary contact structure 16 which includes arcing contact 18, biased to rotate in a clockwise direction, with respect to FIGURE 1, and butt contact 20 positioned to be engaged by arcing and butt contacts 22 and 24, respectively, of the movable contact arm 26 which is pivoted at one end 28 to the lower main terminal 14. An operating rod 30 is pivoted at one end 32 thereof to a central portion of the movable contact arm 26 to cause rotation thereof in response to predetermined overload and/or predetermined instantaneout fault values in a manner well known in the art.

Positioned above the contact structure thus described is an arc chute 34 comprising a plurality of main arc plates 36, preferably ceramic, which include (as shown in FIGURE 2) slits 38 alternately disposed on adjacent arc plates to provide a tortuous path to extinguish an are which is urged up into the arc chute 34.

Arc chute 34 includes rear and front arc runners 40 and 42, respectively, spaced at opposite interior ends thereof, rear arc runner 40 being electrically connected to the upper main terminal 12 at its lower inwardly turned portion 41, and front are runner 42 having an inwardly turned portion 43 which is electrically connected through conductive member 44 to the lower main terminal 14.

Arc chute 34 further includes a vertically disposed transfer gap assembly 46 positioned between two adjacent main arc plates 36' and 36" at a predetermined location with respect to the contact structure including contacts 18, 20, 22, 24 and with respect to the front and rear arc runners 42 and 40.

Transfer gap assembly 46 includes rear transfer gap arc runner 48 and front transfer gap arc runner 50, the detailed construction of which will be described with respect to FIGURE 2, separated by a plurality of arc plates 52 which are preferably identical to the main arc plates 36 and therefore would include alternately disposed slits to aid in the extinguishment of an arc drawn between the transfer gap arc runners 48 and 50.

Circuit breaker 10 further includes a face wound blow out coil 54 which is disposed on at least one surface 56 of the circuit breaker in a configuration which defines an area 57 encompassing the cooperating contact structure, the front and rear arc runners 42 and 40, and a major portion of the transfer gap arc runners 48 and 50. Face wound blow out coil 54 includes a plurality of turns 58 of conductive material, the ends of which are electrically connected at 60 and 62 by suitable fastening means to the front and rear transfer gap arc runners 50 and 48, respectively. Preferably, the connections 60 and 62 are made outside of the area 57 encompassed by the face wound blow out coil 54 so as to improve the dielectric integrity of the entire assembly.

As is taught in U.S. Patent 3,070,681, issued to I. D. Wood on Dec. 25, 1962, which patent is assigned to the assignee of the instant invention, current flow through the turns 58 of the face wound blow out coil 54 generates magnetic flux in the area 57 to urge an arc drawn between arcing contacts 18 and 22 into the arc chute 34 for extinguishment thereof.

Thus with the movable contact arm 26 in its closed position, and without the occurrence of a fault, the current path through the circuit breaker 10 comprises upper terminal 12, stationary contact structure 16, including arcing and butting contacts 18 and 20, movable contact arm 26, and lower terminal 14.

Upon the occurrence of a predetermined fault, operating rod 30 begins to rotate movable contact arm 26 from its solid line position, in FIGURE 1, to the dotted line position 26'. As indicated previously, arcing contact 18 is biased (by means not shown) in a clockwise direction with respect to FIGURE 1 such that arcing contacts 18 and 22 remain in contact for a short time after butt contacts 20 and 24 have separated. As the arcing contacts 18 and 22 are finally separated, an arc is drawn therebetween with the natural expansion caused by the detonation of such are and the flux created thereby urging the arc to a position shown as dotted line 64, in FIGURE 1, wherein the first end 66 thereof is transferred to the lower portion 41 of the rear arc runner 40; the second end 68 thereof remains on the movable contact arm 26 at its position 26'; while a central portion 70 thereof extends between the lower extending portions 72 and 74 of the transfer gap arc runners 48 and 50. Further movement of movable contact arm 26 to its dotted line position 26", in FIGURE 1, causes the end 68 of arc 64 to be transferred to the inwardly turned portion 43 of front are runner 42.

Simultaneously, the existence of arc portion 70 between transfer gap arc runners 48 and 50 initially introduces (by means of electrical connections 60 and 62), the blow out coil 54 into electrical parallel therewith. Subsequently, the flux generated by the turns 58 of coil 54 through area 57 interacts with the entire arc extending between the front and rear runners 40 and 42, including central arc portion 70 such that central portion 70 is urged into arc plates 52 for extinguishment thereof, while the portions of the are extending between the transfer gap arc runners and the front and rear arc runners are simultaneously urged up into the arc plates 36 on both sides of transfer gap assembly 46 for extinguishment. When the central arc portion 70 has been completely extinguished by are plates 52, the turns 58 of the blow out coil 54 now remain in electrical series with the remainder of the arc and are capable of generating maximum flux to urge the remaining portions of the are into arc plates 36. It is noted that since the transfer gap assembly 46 uses standard ceramic arc plates 52, similar to are plates 36, the quantity of arc voltage available during interruption for transfer of the fault current into the blow out coil 54 is much higher than the voltage which would be available in the earlier metal plate versions of'the gap, as shown in Dickinson et al.

As noted above, the transfer gap assembly 46 is located at a predetermined position relative .to the cooperating contacts and relative to the rear arc runner 40. Specifically, as will be apparent from FIGURE 1, the transfer gap assembly 46 is located immediately above the separating contacts so as to materially reduce the amount of time required for the arc to transfer from the lower portion '41 of arc runner 40 to the rear transfer gap arc runner 48. It is apparent that the quicker the transfer between such members, the quicker the blow out coil 54 can be introduced into the circuit, and the quicker the arc can thereby be urged into arc chute 34 for extinguishment. This arrangement is to be contrasted with the Frink patent wherein the transfer gap assembly is effectively positioned at the rear end of the arc chute assembly thereby increasing the time of arc transfer from the separating contacts to the transfer gap assembly-and thereby increasing the total time for are extinguishment.

With respect to the positioning of the transfer gap 'assembly 46 relative to the rear arc runner 40, it may be seen that such assembly is positioned closer to the rear arc runner 40 than the front are runner 42. In the preferred embodiment of the instant invention the transfer gap assembly 46 would be positioned approximately onequarter of the distance between the rear and front are runners 40 and 42, respectively. As noted above, the purpose of such location is to reduce the potential difference existing between the rear arc runner 40 and the rear transfer gap arc runner 48 and thereby reduce the possibility of restrike therebetween.

Specifically, it will be appreciated that since the rear arc runner 40 is electrically connected to terminal 12 while the front are runner is electrically connected to terminal 14, the total system voltage existing between terminals 12 and 14 will be impressed across arc runners 40 and 42; and therefore, the voltage appearing between rear arc runner 40 and rear transfer gap are runner 48, and front are runner 42 and front transfer gap arc runner 50 will be approximately proportional to the position of the transfer gap assembly 46 within the arc chute 34. Thus, by positioning the transfer gap assembly 46 at approximately 25% of the distance between the rear arc runner 40 and the front are runner 42, the potential appearing between rear arc runner 40 and rear transfer are runner 48 will be appoximately only one-quarter of the system potential (neglecting the potential existing between front and rear transfer are runners 48 and 50). This is to be contrasted with the Dickinson et al. arrangement wherein the potential between the rear arc runner and the rear transfer are runner would be approximately one-half of the total system potential and thus the possibility of restrike between these two members significantly greater than the possibility of restrike in the instant invention.

After interruption, since the ends of the turns 58 of blow out coil 54 are electrically connected to the transfer gap arc runners 48 and 50, the blow out coil 54 is electrically isolated from either the upper or lower terminals 12 and 14. Thus, although such coil may be capacitively coupled to either of such terminals to float to some potential dependent upon the potential appearing on such terminals, the blow out coil is not forced to float to that very potential which appears on the upper terminal 12 of the breaker. It becomes apparent therefore that the portion 71 of the blow out coil 54 which isih close proximity to the front are runner will have less of a potential difference with respect to front runner 42 than would be present if the blow out coil 54 had been electrically connected to the high potential terminal 12. With a smaller potential gradient existing between the portion 70 and the front arc runner 42, the possibility of corona formation is materially reduced and also the ultimate possibility of restrike between these members is virtually eliminated.

Referring to FIGURE 2, there is shown an exploded perspective view of a preferred embodiment of the transfer gap assembly 46. It will be seen that the front and rear transfer are runners 50 and 48, respectively, include a generally W-shaped configuration having opposed upstanding legs 72' and 74', and a centrally located upstanding portion 76 spaced centrally therebetween. Central portion 76 extends above the arc chute assembly 34, in FIG URE 1, whereby the connections 60 and 62 may be easily made thereto. Insulated sheets 78 and 80 are spaced between upstanding portions 72 and 76 and 76 and 74.

Thus there has been described a circuit breaker which includes a face wound blow out coil and a vertically disposed transfer gap assembly which is located at a predetermined position with respect to the separating contacts of the breaker, and with respect to the rear arc runner thereof, so as to minimize the time required for transfer of an are between the separating contacts and such vertical transfer gap assembly and to minimize the potential appearing between such transfer gap assembly and the rear arc runner. Furthermore, the transfer gap assembly includes ceramic arc plates and is so positioned within the area of the face wound blow out coil to materially aid in extinguishment of an arc existing between the transfer are runners of the assembly and thereby hasten the complete series introduction of the blow out coil into the arcing circuit. Additionally, after the interruption, the face wound blow out coil is free to float to a potential which is not necessarily the potential appearing on the high potential terminal of the circuit breaker, and as a result thereof the potential gradient on the air between the blow out coil and the front are runner is substantially reduced to prevent corona formation thereof and ultimate breakdown of the space between such members.

It is noted that during tests of a 15 kv. circuit breaker constructed in accordance with the above noted features, the critical impulse level was found to increase from about 92 kv. for the conventional arc chute to 130 kv. for an arc chute utilizing the interposed vertical transfer gap assembly.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.

What is claimed is:

1. A circuit breaker comprising:

first and second circuit breaker terminals capable of having a potential difference existing therebetween;

stationary contact structure secured to one end of said first circuit breaker terminal, said stationary contact structure including an arcing contact portion;

a movable contact arm pivotally secured to one end of said second circuit breaker terminal, said movable contact arm including an arcing contact normally abutting said arcing contact portion;

an arc chute positioned above said stationary contact structure and movable contact arm to extinguish an are drawn between said arcing contact portion and said arcing contact upon separation thereof, said are chute including a plurality of main arc plates of nonconducting material;

first and second arc runners positioned at opposite interior ends of said are chute, said first arc runner being electrically connected to said first circuit breaker terminal, said second arc runner being electrically connected to said second circuit breaker terminal, said arcing contact portion of said stationary contact structure and said arcing contact of said movable contact arm being located below said are chute but intermediate said ends thereof;

energizable magnetic blow out means positioned adjacent said are chute for urging said are into said are chute;

a transfer gap means including first and second elongated conductive transfer gap runners spaced apart by a plurality of arc plates which are of identical construction as said main arc plates; and

said vertically disposed transfer gap means positioned within said are chute between said first and second arc runners and directly vertically above said arcing contact portion for intercepting said are to energize said magnetic blow out means, said transfer gap means being positioned between two of said main arc plates at about one quarter of the distance between said first and second arc runners and closer to said first arc runner than said second arc runner.

2. The circuit breaker of claim 1, wherein said magnetic blow out means comprises a face wound blow out coil having first and second ends electrically connected to said first and second transfer gap runners, respectively, said coil being arranged in a predetermined configuration to define an enclosed area which encompasses said first and second transfer gap runners whereby magnetic flux generated by said coil, upon energization thereof, will pass through said transfer gap means.

References Cited UNITED STATES PATENTS 2,821,606 1/1958 Mikos et al 200-147 2,590,602 3/1952 Frink 200147 3,201,551 8/1965 Mercier 200-447 ROBERT S. MACON, Primary Examiner. 

